A study of seasonal variation in butter-fat

Abstract

The yellow color and blue values determined on the non-saponifiable residue were in good agreement with the well established variation of the carotene and vitamin A contents of butter with the quantity of green fodder in the diet. The blue values of the untreated butter-fat were valueless as a guide to vitamin A content. The total vitamin A activity of summer butter-fat from shorthorn cows appeared to be some three times as great as that of winter butter-fat; the activity due to carotene was also greater.